KIEV, Ukraine (AP) -- Mikhail Khodorkovsky, once Russia's most famous prisoner, has harshly criticized Russian President Vladimir Putin over the annexation of Crimea and Russian pressure against Ukraine.

Khodorkovsky, who spent 10 years in prison in a case widely seen as political revenge by Putin, opened a conference in Kiev devoted to fostering ties between Ukraine and Russia. He said Thursday that Putin was being petty and vengeful against a democratic uprising and that he and many other Russians are opposed to Putin's policies on Ukraine.

He also said "no dictator, however powerful he is, can turn us into enemies."

Participants at the conference included the most prominent Kremlin critics and thinkers. Khodorkovsky also suggested that major changes await Russia "and the wildest dreams today become reality tomorrow."